There are a number of different devices or systems for conducting electrical current between a rotating current-carrying component and a contacting stationary conductor. Some include familiar systems employing conventional slip-rings, commutators or the like. Other systems, similar to that disclosed in U.S. Pat. No. 388,513 (Van Gestel) use gearing systems that provide electrical conduction through intermeshing gears. Such systems are relatively expensive to manufacture, cumbersome to assemble and use, and due to wear, are unreliable and inefficient after extended use at high rotational speeds. In addition, because it is difficult to maintain positive meshing of the gears, sparking and heating problems often result.
Another approach, which is of particular interest here and which is disclosed in U.S. Pat No. 3,769,535 (Bates), uses a wire brush disc mounted with its axis parallel to the axis of the rotating shaft. The shaft has a metallic disc having a smooth edge mounted thereon, and the wire brush is positioned such that the tips of the wire bristles engage and rub against the edge of the metallic disc. This approach has a number of drawbacks. For example, because both discs rotate in the same plane, it is necessary that the brush fibers be deformed and then compressed as they pass the tangent point. The closer the discs are positioned to each other, in order to increase their contact, the greater the deformation of the brush fibers. Thus, such a system requires minimal contact if the wear on the brushes is to be minimized. Because of the low frictional forces between the discs, it is often required to have a separate rotational drive source for the brush disc in order to keep the disc in motion, especially at low speeds. A further significant drawback, and one that is common to "gearing" systems as well, is that these systems require an electrical "brush" contactor, (a conventional wiper brush which makes contact with a gear, in van Gestel, and a disc brush, in Bates). Conventional wiper brushes suffer from severe wear problems and provide poor contact at high rotational speeds.